The renal collecting system, from the inner medullary collecting duct (IMCD) to the trigone of the bladder, is derived from the ureteric bud (UB). To achieve this, the UB differentiates into various cell types that form structurally distinct parts of the urinary tract. The ability of the UB to differentiate into different cell types is in part determined by the expression of developmentally regulated proteins in a spatio-temporal pattern. Cell lines have been developed from both mouse UB and IMCD. In this proposal we intend to identify cell membrane proteins that are specifically expressed on UB cells and not IMCD cells, thus determining molecules that play a role in UB development. The following approach will be undertaken. 1) Production of subtractive monoclonal recombinant and hybridoma antibodies that are immunoreactive against UB but not IMCD cells. Phage-displayed recombinant antibody libraries and B cells derived from immunized rats will be used to produce these antibodies. 2) Selection of antibodies that react with UB and not IMCD cells at a functional level. 3) Determination of the antigens. against which the antibodies identified in aim 2 are directed. Our goal is to identify either novel or previously described molecules that are necessary for UB development. If the molecules are completely novel we will determine their functional properties both in general as well as in regulating UB development. If the proteins are already described we may be able to ascribe a new function to them in terms of UB development.